LU-6142 lfsck: make all 'struct lfsck_operations' to const

LU-6142 lfsck: make all 'struct lfsck_operations' to const

Operations structures should be 'const' wherever possible.
So change both lfsck_operations and lfsck_assistant_operations
to const.

Test-Parameters: trivial
Signed-off-by: Mr NeilBrown <neilb@suse.de>
Change-Id: Ic457c0e52ceafab58cb788db383957ed4ab39df4
Reviewed-on: https://review.whamcloud.com/39397
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Lai Siyao <lai.siyao@whamcloud.com>
Reviewed-by: Arshad Hussain <arshad.hussain@aeoncomputing.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>